Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D37/00—Processes of filtration
  • B01D37/02—Precoating the filter medium; Addition of filter aids to the liquid being filtered

Definitions

• the invention relates to a process for the reduction in size of the pores of a filter medium for beverages, preferably beer.
• the object of the filtration process in the beverages industry is to filter turbidity-causing particles and micro-organisms out of the beverage before it is decanted. It is an essential factor in the beverages industry since the consumer expects a brilliantly clear beverage. Clear filtration is, however, also required for reasons of microbiological stability. All micro-organism cells must be removed from the beverage. This is ensured only if completely clear filtration has taken place.
• a group of these prior-art processes is characterized in that the beverage is passed through a prefabricated filter cake, e.g. of cellulose, or through a prefabricated filter bed of fibre materials of diverse origins.
• the other group of prior-art filtering processes is characterized in that settling filtration is carried out.
• pulverulent filter materials are quantitatively added to the flow of liquid.
• the finely particled filter aids added are subsequently again removed from the flow of liquid via screens or fibre beds. Kieselguhr or cellulose powder, or mixtures thereof, are principally used for settling filtration.
• the size of the pores is dependent on the filter material used, its particle fineness and possibly its fine structure.
• the use of kieselguhr as filter medium is particularly advantageous because the means are provided by the selection of suitable types of kieselguhr to adjust both the flow rate and the degree of filtration to the respective requirements. Nevertheless, it does occur in the case of some applications that even the finest kieselguhr cannot hold back turbid components of the beverage.
• pores within the meaning of the concept can, for example, be fine structures within the individual particles forming the filter medium (e.g. in the case of kieselguhr), or even interspaces, for example between fibres which form the filter medium.
• Cellulose fibres which are also utilized for the filtration of beverages, form readily permeable filter beds; they are, however, not suitable in many instances for clear filtration because they cannot hold back finely particled turbidity-causing substances. In the past, therefore, cellulose was compacted with asbestos fibres. Since it is necessary to refrain from the use of asbestos for health reasons, attempts are made to increase the degree of filtration by the admixture of kieselguhr. The utilization of cellulose on its own would be advantageous in that the filter medium could be used as feed after use by admixing it, for example, to drafts. This is, however, not possible if kieselguhr in any appreciable quantity is contained in the cellulose.
• Silicic-acid hydrogels in pulverulent form has also already been recommended as filter aids for settling filtration.
• Silicic-acid hydrogel is actually used for protein stabilization of beer. Its object is to remove instable colloids from the beer by adsorption. This takes place practically during the filtration of the beer, when the hydrogel is quantitatively added with the kieselguhr filtration to the beer and is again separated in the filter.
• settling filtration be carried out using only silicic-acid hydrogel, and to dispense with the kieselguhr or other filter aids. This, however, involves considerable difficulties.
• Powdery synthetic products could also be considered as filter materials, such as have been developed not for filtration but for the adsorption of polyphenolic compounds from beverages, such as, e.g. PVPP or polyamides.
• precoating filters they can be used like kieselguhr, but are of minor value as filter aids because they do not permit clear filtration.
• a prerequisite for the utilization of these fibres would, however, be that, prior to use, they had been washed so as to be free of substances which are soluble in the beverage to be filtered.
• the advantage of these polymer filter media would reside in that, after filtration, they could be regenerated by simple scouring using, for example, dilute soda lye. Application thereof, however, likewise fails since clear filtration cannot be obtained.
• the object of the invention is to propose a process of the kind mentioned at the outset by means of which the size of the pores of a filter medium can, in a simple manner, be reduced and adjusted to the requirements.
• this object is met in that, upstream of the filter medium through which passes the beverage, continuously or in a batch-feed process using a tank, silica sol is added in such a quantity and controlled such that the silicic-acid precipitation, i.e. the transition from SiO 2 primary particles to SiO 2 secondary particles, has taken place before the beverage has left the filter medium, and the resultant silicic-acid precipitation reduces the size of the pores without sealing them.
• the invention is applied in particular within the framework of a settling-filtration process, whereby the silica sol is added in such a quantity and in such a proportion relative to the filter medium that an adequate filtering effect is achieved without the pores of the filter medium being constricted or completely obstructed.
• the SiO 2 secondary particles resulting from the silica sol swell to a certain size so that they are held back in the filter medium in order to reduce the size of the filter pores. It is thus possible to hold back even finely particled turbid components of the beer in the filter medium.
• Essential in the case of the process according to the invention is that, in contrast to the state of the art, the silicic-acid flocculation is not removed, but rather that it serves to reduce the size of the filter pores during filtration of the beverage in the filter, in conformity with the object according to the invention.
• the silica sol is added only in a small quantity.
• the silica sol is used in a quantity (calculated as SiO 2 ) of 0,5-20 g of SiO 2 /hl of liquid (5-200 ppm), preferably 1-10 g/hl (10-100 ppm) and in particular 2-8 g/hl (20-80 ppm).
• the ratio of the quantity of silica sol to the filter medium is easily established by the specialist in the field depending on the applicable factors, in particular the type of filter material.
• the process according to the invention in particular permits the use in the beverages industry of such filter media which, in effect, have too coarse a pore structure to ensure fine filtration, such as the above-mentioned cellulose fibres, starch, silicic-acid hydrogels, powdery or fibrous synthetic products, and the like.
• the practical execution of the process according to the invention can be such that, e.g., the intended quantity of silica sol is added to the beverage in the storage tank, e.g. some hours prior to the proposed filtration. Until that process, the silicic-acid precipitation has completely developed. Depending on the size of the storage tank, it is still in suspension, with the result that the process according to the invention can immediately be commenced. If necessary, however, thorough mixing can be provided by the injection, e.g. of carbon dioxide.
• a different embodiment of the present invention comprises the treating of a partial quantity of the beverage to be filtered with silica sol, awaiting the development of flocculation and maintaining uniform distribution by suitable means. This partial quantity is then mixed with the remaining beverage to be filtered immediately upstream of the filter.
• the silicic-acid flocculation should not settle, in contrast to the processes according to the state of the art, but should be uniformly distributed in the beverage to be filtered.
• the process according to the invention can, however, also be carried out in that the silica sol is quantitatively added to the wort. Then it is necessary to ensure the required reaction time, optionally by the inclusion of a buffer tank between silica-sol addition and filter. If the operation takes place without a buffer tank, it is expedient at first to switch the filter into circulation (cyclic flow?). It is then possible to perceive whether the required compacting of the pores has taken place by the reduction of the degree of turbidity of the filtrate.
• aqueous gelatine solution is added to the beverage in addition to the silica sol. This results in a more rapid formation of the silicic-acid precipitation and also an influencing of the size of the flakes of the precipitate.
• An aqueous solution of polyvinyl pyrrolidone (PVP) can also be used as flocculation aid instead of an aqueous gelatine solution.
• Silica sol modified with aluminium compounds can advantageously be added.
• the filter medium can be composed of kieselguhr, cellulose, starch, silica gel and/or pulverulent or fibrous polymers which are insoluble in water.
• silica sol for the clarification of beverages and also beer is known, e.g. from DE-OS No. 2 133 906, U.S. Pat. No. 3,878,300, DE-OS No. 3 304 437 and numerous other publications.
• the silica sol is, however, used in a fundamentally different process and also with a different action mechanism.
• the process according to the invention also differs from prior-art processes in that it is completely without regard for the occurrence or absence of adsorption processes on the SiO 2 precipitations resulting from silica sol. It is sufficient if, after the addition of the silica sol to beer or other beverages, a precipitation of SiO 2 secondary structures takes place which are held in the pores of a filter medium. As a result, it is possible to reduce the size of the pores of the filter medium such that all turbidity-causing particles, which are larger than the pores, are held back, irrespective of adsorption processes.
• silica sol within the scope of the present invention, preferably designates stabilized silica sols which are produced according to one of the following three processes:
• the processes are described in Ullmann, Volume 21, 1981.
• the stabilization of the silica sols can be carried out, for example, by the addition of controlled quantities of sodium hydroxide or other basic (alkaline?) substances.
• a small-scale test is carried out, in which unfiltered entire beer from a Munich brewery is subjected to precoating filtration on laboratory scale using various filter aids.
• the duration of filtration in respect of specified filtrate volumes is established and a filtering factor calculated therefrom, which represents a measure for the speed of filtration (K. Raible and H. Bantleon, "Monatszeitschrift fur Brauerei 1968", pp. 277-285).
• the very finely filtering kieselguhr Filtercel serves as filter aid, and, by way of comparison, a powdery PVPP product. Since this PVPP product does not permit clear filtration, 10 ml/hl and 20 ml/hl silica sol are added in further parallel tests.
• the silica sol has a specific surface of 100 m 2 /g and 30% by mass of SiO 2 .
• the above test demonstrates as to how, as a result of the utilization according to the invention of silica sol for the compacting of the filter cake, the means is provided to utilize an adsorption means, which was actually designed only for protein stabilization, also as a complete filter aid.
• the PVPP is washed with dilute soda lye to be freed of the adsorbed polyphenolic compounds.
• the small quantity of silicic acid from the silica sol and deposited in the filter cake is dissolved and is again removed from the PVPP powder.
• the PVPP can again be used for filtration and stabilization.
• Example 3 A laboratory test is carried out under the same test conditions as given in Example 3. The comparison is by means of the filtration properties of potato starch with simultaneous addition of 10 ml/hl silica sol. The results of this test are set out in the Table:
• the clearly filtering kieselguhr Filtercel provides a filtering factor of 1,15 and a clarity of the filtrate of 0,60 EBC units.
• filtration with pulverulent potato starch produces a filtering factor of 0,45.
• the beer is, therefore, filterable three times as rapidly using starch than with Filtercel.
• the clarity of the filtrate of 1,9 EBC units however precludes the use of the starch as filter aid.
• the starch After filtration, the starch can be used as feed. 3,6 g SiO 2 are present in 100 g starch from 10 ml/hl of 30% silica sol. Since the used filtration starch is, in any event, used as feed together with the draffs, the small silicic-acid component is nutrition-physiologically insignificant and, moreover, not detectable during feedstuffs analysis.
• the suitability of polyacryl nitrile hollow fibres as aid in beer filtration is examined. Available is a test product detx 2,2/0,6 mm. The length of the individual fibres is 0,6 mm, the outside diameter of the hollow fibres approximately 20 u.
• the polyacryl nitrile is resistant to dilute alkaline solution and acid and could, therefore, be included as filter aid capable of being regenerated.
• the advantage of the utilization of the synthetic fibres in comparison with the filtration using kieselguhr, resides in that the synthetic fibres can be washed with dilute soda lye and, after rinsing of the lye, can again be used for filtration.
• the beer to be tested is cooled to 0° C., and subsequently small-scale filtration is carried out.
• the following are used:
• the silica sol having a specific surface of 100 m 2 compacts the Lucilite filter cake only relatively little, since the filter-cake factor increases only from 0,25 to 0,35. Nevertheless, a distinct improvement of the clarity of the filtrate is observed.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Distillation Of Fermentation Liquor, Processing Of Alcohols, Vinegar And Beer (AREA)
• Filtering Materials (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)

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Citations (13)

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• 1988
  • 1988-06-15 DE DE3820393A patent/DE3820393A1/de active Granted
• 1989
  • 1989-01-16 EP EP89100660A patent/EP0325188B1/de not_active Expired - Lifetime
  • 1989-01-16 ES ES89100660T patent/ES2065927T3/es not_active Expired - Lifetime
  • 1989-01-16 DE DE58908807T patent/DE58908807D1/de not_active Expired - Lifetime
  • 1989-01-17 DK DK019589A patent/DK19589A/da not_active Application Discontinuation
  • 1989-01-18 JP JP1007892A patent/JPH084694B2/ja not_active Expired - Fee Related
  • 1989-01-18 US US07/298,518 patent/US5008018A/en not_active Expired - Lifetime
  • 1989-01-18 AU AU28590/89A patent/AU610332B2/en not_active Ceased

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